Users of test and measurement instruments, such as oscilloscopes, often use probes to connect a device-under-test (DUT), such as a circuit board, to an input of a test and measurement instrument in order to visualize and perform measurements of electrical signals occurring in the DUT. These users are typically engineers designing circuit boards for a wide variety of electronic devices. Consumers of electronic devices generally desire these devices to be as physically small as possible. Accordingly, engineers are often tasked with packing a high quantity of electrical components into a small circuit board area. Additionally, the electrical components themselves are generally designed to be physically smaller with each successive generation. The small size and high density of electrical components in a DUT can make it challenging for engineers to probe test points on a DUT.
Therefore, test and measurement probes must be able to make electrical contact with DUT test points that can be difficult to access, while still providing high bandwidth and good signal fidelity. Test points in a DUT vary considerably in geometry and accessibility. They may reside in a DUT in every angle of orientation from horizontal to vertical. They may be obscured by electrical components. Contemporary high-speed signal busses, such as DDR2, DDR4 and PCIe Gen 4, among others, often use differential signaling, requiring that a probe used to measure these signals must be able to make simultaneous electrical contact with two test points. This may be even more challenging if the two test points are on different planes.
Sometimes a probe may be semi-permanently attached to DUT test points. For example, a “solder-down” type probe may have wires from the probe that are soldered to test points, or that are attached to test points with conductive epoxy. This kind of semi-permanent probe attachment scheme can provide a reliable connection to the DUT. However, solder-down probes also have a number of disadvantages. Due to the often poor accessibility of the DUT test points, the process of soldering probe wires to the DUT can be challenging for a probe user, requiring long set-up times and exceptional dexterity. Further, inconsistencies in the quality of the solder connection can cause high variability in signal fidelity, especially at upper frequencies. Additionally, the small gauge of wire used to attach the probe makes it easy for a user to potentially damage the DUT when soldering the wires in place. In order to probe a different set of test points, a user must unsolder and re-solder the wires—a time-consuming process making this type of probe unsuitable for fast debug environments in which a user may need to quickly check several different DUT test points. Finally, this type of solder-down probe tends to wear out after only a few connections, and can be expensive to replace.
To overcome some of these issues, another style of probe, known as a “browser probe,” is designed to be held in a user's hand, or with a holding tool, and be positioned by the user to touch one or more test points in a DUT. This type of browser probe is better suited for debug environments in which maximum probe placement flexibility and minimal measurement setup time are desirable. A browser probe may be designed as a single-ended probe, which measures the electrical signal at one test point in a DUT with respect to a ground, or may be designed as a differential probe, which measures electrical signals at two test points in a DUT and produces an output signal based on the difference between the two measured signals.